This invention relates in general to vehicle brakes and, in particular, to an improved vehicle disc brake rotor.
A conventional hydraulic disc brake assembly includes a brake caliper and a rotor. The brake caliper is secured to an unsprung suspension component of the vehicle, and includes a pair of brake friction pads and a hydraulically actuated piston. The rotor is rotatably supported with an associated wheel relative to the caliper, and includes a mounting flange and an outer annular friction disc. The friction disc defines generally parallel machined inner and outer faces adapted to be frictionally engaged by the friction pads during vehicle braking.
Several important criteria must be considered in designing a rotor for a given brake application. One such criterion is the thermal capacity of the rotor to adequately absorb heat generated during a given vehicle stop. A second, but related criterion is the ability of the rotor (after a given stop) to sufficiently cool to a safe operating temperature for the next vehicle stop or stops. These two criteria are not necessarily mutually exclusive. A solid one piece "unvented" rotor may provide sufficient mass and heat capacity to adequately absorb all the heat generated during a single, hard vehicle stop; however, it may not have sufficient cooling capabilities to adequately handle a series of subsequent hard vehicle stops. Similarly, an unvented rotor with sufficient cooling capabilities may not have sufficient mass to function as an adequate heat sink during a given stop.
While solid unvented rotors exhibit superior heat sink properties, they are generally not equipped to handle a series of hard stops, since their cooling capabilities are limited. In order to dissipate the heat generated during a previous stop, it is known to provide the rotor with a "vented" design.
One example of a vented rotor is shown in U.S. Pat. No. 4,083,435 to Gallus et al. As shown in this patent, the friction disc includes a pair of mutually spaced apart brake friction plates which are connected together by a plurality of radial fins. The fins cooperate to form radially extending air cooling channels to aid in dissipating the heat generated during braking. Other examples of vented rotors are disclosed in U.S. Pat. No. 3,298,476 to Day, U.S. Pat. No. 4,102,438 to Rancourt, U.S. Pat. No. 4,379,501 to Hagiwara et al., U.S. Pat. No. 4,865,167 to Giorgetti et al., U.S. Pat. No. 4,641,731 to Kawaguchi et al., and U.S. Pat. No. 4,757,883 to Thiel et al.
Typically, the brake caliper includes radially extending and axial spaced fingers for supporting the outboard brake pad. The outer radial ends of the fingers are connected by a bridge or center portion. This structure causes the fingers to become less stiff in the radially inwardly direction. As a result of this, the caliper fingers tend to flex during braking, causing the brake pads to apply a greater braking pressure at the outer radial portion of the rotor. Thus, the rotor must be designed such that the outer radial portion thereof is sufficiently stiff or rigid so as to accommodate the associated increased brake forces in this region.
The conventional way to increase the stiffness of the outer radial portion of rotor is by uniformly increasing the thickness of the brake friction plates. However, the thickness of the friction plates is limited by the clearance between the friction pads. Also, increasing the thickness of the friction plates adds additional rotating mass and unsprung weight to the vehicle, and thus adversely affects the performance, handling, and fuel economy of a vehicle. In addition, increasing the thickness of the friction plates unnecessarily stiffens the rotor at the hat portion.
Another way to increase the stiffness of the outer radial portion of the rotor is shown in U.S. Pat. No. 5,161,652 to Suzuki. As shown in this patent, both of the friction plates are directly attached at their inner ends to the hat portion of the rotor.
A further way to increase the stiffness of the outer radial portion of the rotor is shown in German Patent DE 3,908,655. As shown in this patent, the inner surfaces of each of the friction plates is provided with spaced apart reinforcing ridges near the outer radial portions thereof.